Neural regeneration and plasticity will be studied in female rats (200-250g) during a six month period after either frontal (FC), lateral-frontal (LFC), complete (CC) or sham hypothalamic cuts produced by the stereotaxic placement of a small Halasz-type knife. Parameters selected for investigation are neuroendocrine function, hypothalamic neurotransmitter content, sex behavior and arcuate nucleus synaptic profiles. Postoperative intervals chosen for study (1 hr, 2,7, 14, 21, 75, and 180 days) will be similar for all parameters and in certain cases the same animal will furnish data for several studies. Functional preoptico-tuberal-hypophyseal connections remaining postoperatively will be evaluated using bilateral electrochemical stimulation (ECS) of the medial preoptic area rostral to all lesions. Pituitary release of luteinizing hormone (LH) after ECS will be estimated by radioimmunoassay (RIA) of plasma LH during a 160 min post-stimulation period. The presence of tubal ova and ovarian morphology 18hr after ECS will be used to substantiate RIA estimates of plasma LH concentrations. Hypothalamic fragments dissected after decapitation of the latter animals will be assayed radiometrically for norepinephrine and acetylcholine concentration. In another group of rats, sex behavior after frontal deafferentation (FC) will be quantitated by calculating the percentage of lordosis responses to mounts by males on postoperative days 7, 14, 21, 75 and 180. The role of ovarian estrogens in behavioral response to FC will also be studied in ovariectomized (OVX) - FC females and OVX -FC rats that receive estrogen for 30 days after FC. In addition, a quantitative and qualitative synaptic profile for cells in the arcuate nucleus of the hypothalamus removed at the intervals of study from animals in both the reproductive function and behavior studies will be assembled from electron micrographs of selected arcuate regions.